I either forgot or never knew there's a difference between ".class1.class2" and ".class1 .class2" (without and with a space). I didn't even think the first is v

I either forgot or never knew there's a difference between ".class1.class2" and ".class1 .class2" (without and with a space). I didn't even think the first is valid. That bit alone was worth the entire article for me.